I have a late 2008 MacBook Pro with a CUDA enable GPU, I have enabled the GPU to run always in my default preferences.

When Boinc starts the following is reported;

Tue 5 Jan 21:53:21 2010 Starting BOINC client version 6.10.21 for x86_64-apple-darwin
Tue 5 Jan 21:53:21 2010 log flags: file_xfer, sched_ops, task
Tue 5 Jan 21:53:21 2010 Libraries: libcurl/7.19.4 OpenSSL/0.9.7l zlib/1.2.3 c-ares/1.6.0
Tue 5 Jan 21:53:21 2010 Data directory: /Library/Application Support/BOINC Data
Tue 5 Jan 21:53:21 2010 Processor: 2 GenuineIntel Intel(R) Core(TM)2 Duo CPU P8600 @ 2.40GHz [x86 Family 6 Model 23 Stepping 6]
Tue 5 Jan 21:53:21 2010 Processor features: FPU VME DE PSE TSC MSR PAE MCE CX8 APIC SEP MTRR PGE MCA CMOV PAT PSE36 CLFSH DS ACPI MMX FXSR SSE SSE2 SS HTT TM SSE3 MON DSCPL VMX SMX EST TM2 SSSE3 CX16 TPR PDCM SSE4.1
Tue 5 Jan 21:53:21 2010 OS: Darwin: 10.2.0
Tue 5 Jan 21:53:21 2010 Memory: 4.00 GB physical, 27.65 GB virtual
Tue 5 Jan 21:53:21 2010 Disk: 200.88 GB total, 27.40 GB free
Tue 5 Jan 21:53:21 2010 Local time is UTC +0 hours
Tue 5 Jan 21:53:21 2010 No usable GPUs found
Tue 5 Jan 21:53:21 2010 Not using a proxy
Tue 5 Jan 21:53:21 2010 rosetta@home URL http://boinc.bakerlab.org/rosetta/; Computer ID 1049197; resource share 100
Tue 5 Jan 21:53:21 2010 climateprediction.net URL http://climateprediction.net/; Computer ID 968718; resource share 100
Tue 5 Jan 21:53:21 2010 Einstein@Home URL http://einstein.phys.uwm.edu/; Computer ID 1914793; resource share 100
Tue 5 Jan 21:53:21 2010 Milkyway@home URL http://milkyway.cs.rpi.edu/milkyway/; Computer ID 64500; resource share 100
Tue 5 Jan 21:53:21 2010 SETI@home URL http://setiathome.berkeley.edu/; Computer ID 4883082; resource share 100
Tue 5 Jan 21:53:21 2010 SETI@home General prefs: from SETI@home (last modified 05-Jan-2010 21:43:03)
Tue 5 Jan 21:53:21 2010 SETI@home Computer location: home
Tue 5 Jan 21:53:21 2010 SETI@home General prefs: no separate prefs for home; using your defaults
Tue 5 Jan 21:53:21 2010 Reading preferences override file
Tue 5 Jan 21:53:21 2010 Preferences:
Tue 5 Jan 21:53:21 2010 max memory usage when active: 2048.00MB
Tue 5 Jan 21:53:21 2010 max memory usage when idle: 3072.00MB
Tue 5 Jan 21:53:21 2010 max disk usage: 4.00GB
Tue 5 Jan 21:53:21 2010 max download rate: 102400 bytes/sec
Tue 5 Jan 21:53:21 2010 (to change, visit the web site of an attached project,
Tue 5 Jan 21:53:21 2010 or click on Preferences)
Tue 5 Jan 21:53:21 2010 SETI@home Restarting task 24ja07ab.19433.5389.16.10.19_1 using setiathome_enhanced version 603
Tue 5 Jan 21:53:21 2010 SETI@home Restarting task 24ja07ab.19433.5389.16.10.81_1 using setiathome_enhanced version 603

... why is there NO usable GPUs found? (Bold above)

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Because Nvidia hasn't done 64bit Cuda drivers yet, there are 32bit Cuda drivers available, but the 64bit Boinc can't see them.
See this thread:

Mac user GPU

Slicker at collatz has made a MAC OS X 32-bit CUDA App, but has no-one to test it.

Claggy

Because Nvidia hasn't done 64bit Cuda drivers yet, there are 32bit Cuda drivers available, but the 64bit Boinc can't see them.
See this thread:

Mac user GPU

Slicker at collatz has made a MAC OS X 32-bit CUDA App, but has no-one to test it.

Claggy

Claggy,

there are CUDA apps for Einstein@Home and Collatz for MacOS X. They work and validate o.k.

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Because Nvidia hasn't done 64bit Cuda drivers yet, there are 32bit Cuda drivers available, but the 64bit Boinc can't see them.
See this thread:

Mac user GPU

Slicker at collatz has made a MAC OS X 32-bit CUDA App, but has no-one to test it.

Claggy

Claggy,

there are CUDA apps for Einstein@Home and Collatz for MacOS X. They work and validate o.k.

Yes, i know. :)

MAC OS X 32-bit CUDA App

Claggy